1. Field of the Invention
The present invention relates generally to an improvement in head up display systems and, more particularly, to controlling the transparency of the panel upon which the display is projected so as to compensate for changing ambient light conditions.
2. State of the Art
Head up displays were first created about thirty years ago when the performance of military jet aircraft progressed such that a pilot did not have time to make the required scans of instruments while concentrating on flying during tactical situations. A head up display provides a transparent panel in the pilot's line of sight. The panel is usually set at an angle so that information can be displayed on the screen and read by the pilot. Similar systems are now increasingiy available in automobile, van, and truck vehicles. Vehicle information such as speed, operating gauges, and the like, are projected by an image light typically from a liquid crystal panel to the windshield of the vehicle. While in operation, however, changing ambient light conditions can create glare and wash out the display in sunlight or, in dim light, the display may appear harshly bright.